Most animals comprise millions or billions of cells that multiply and differtiate to form various organs that perform specialized functions. The sea sponge's cells, however, do not differentiate as drastically and do not amass to form organs. This allows the sea sponge to perform a pretty amazing feat.
If a sponge is pushed through a fine mesh or cloth, disassembling it at a cellular level, the individual cells are capable of reforming over time. Separated cells will actively move toward and rejoin with each other, creating thousands of microscopic mini-sponges.
Thus, the most thorough method of destroying a living being is the sea sponge's most powerful method of reproduction.